1. Field of the Invention
The present invention relates to a lens barrel for use in e.g. a projector or a camera, and a projector incorporated with the lens barrel.
2. Description of the Background Art
Conventionally, there has been known a lens barrel comprising a fixed cylinder, and a cam ring which is mounted on the fixed cylinder in such a manner as to be engaged with a lens holding frame for holding a movable lens group and to be rotatable about an optical axis. In the lens barrel, the movable lens group is moved with the lens holding frame in the optical axis direction by rotating the cam ring. In such a cam-driven lens barrel, as shown in FIGS. 19A to 19C for instance, in most of the cases, a stopper pin (projection) 101 formed on a fixed cylinder 100 is contacted with each of a first rotation restricting portion 103a and a second rotation restricting portion 103b formed on a cam ring 102, whereby the lens holding frame is stopped while restricting the rotation of the cam ring 102 at a zoom end.
In the above arrangement, however, since the above operation is performed by the single stopper pin 101, the following drawbacks are involved.
Specifically, in the cam-driven lens barrel, as shown in FIG. 19A, there is formed a slight fitting clearance 105 between the cam ring 102 and the fixed cylinder 100 for securing smooth driving of the cam ring 102. As a result, while the lens barrel is used, the fitting clearance 105 may be shifted to a lower side by the weight of the cam ring 102, and a maximum clearance portion 105a may be located at a lower position. Further, since the direction in which the cam ring 102 is shifted changes by restricting the rotation of the cam ring 102 at one of zoom ends, the position of the largest clearance portion 105a changes. Likewise, since the direction in which the cam ring 102 is shifted changes by restricting the rotation of the cam ring 102 at the other of the zoom ends, the position of the maximum clearance portion 105a also changes. As a result, a decentering direction of the movable lens group resulting from the fitting clearance 105 between the cam ring 102 and the fixed cylinder 100 changes depending on a zoom end, and a decentering amount increases. In particular, optical performance degradation between the zoom ends increases.
More specifically, for instance, as shown in FIG. 19B, if the cam ring 102 is rotated clockwise in the drawing of FIG. 19B, the first rotation restricting portion 103a of the cam ring 102 is abutted against the stopper pin 101 at one of zoom ends, and thereafter, when a force is exerted on the cam ring 102, the cam ring 102 is rotated around the first rotation restricting portion 103a (stopper pin 101) as the center of rotation, and the fitting clearance 105 is shifted to a left side, with the result that the maximum clearance portion 105a is located at a left position. On the other hand, as shown in FIG. 19C, if the cam ring 102 is rotated counterclockwise in the drawing of FIG. 19C, the second rotation restricting portion 103b of the cam ring 102 is abutted against the stopper pin 101, and thereafter, when a force is exerted on the cam ring 102, the cam ring 102 is rotated around the second rotation restricting portion 103b (stopper pin 101) as the center of rotation, and the fitting clearance 105 is shifted to a right side, with the result that the maximum clearance portion 105a is located at a right position opposite to the left position. In FIGS. 19A to 19C, the fitting clearance 105 is illustrated with a large size to simplify the description. Likewise, the drawings of FIGS. 6A to 6C, FIGS. 11A to 11C, FIGS. 16A to 16B, and FIGS. 17A to 17B are illustrated as such.
There is known a technology as proposed in Japanese Unexamined Patent Publication No. 2009-251315 (D1), as a technology for suppressing optical performance degradation resulting from a change in the shift direction of a cam ring with respect to a fixed cylinder at a zoom end. The technology provides an arrangement, wherein decentering resulting from a change in the shift direction due to a fitting clearance is suppressed by covering the cam ring with a tubular member having a projection on the outer circumference thereof for restricting a displacement amount of the cam ring at the projection, whereby optical performance degradation is suppressed.
The technology disclosed in D1, however, is also affected by an engagement state of a connecting portion between the fixed cylinder and the tubular member formed on the outer circumference of the cam ring. In other words, in the technology disclosed in D1, it is essentially required to define a clearance between the cam ring and the tubular member to an amount equal to or smaller than the displacement amount of the cam ring with respect to the fixed cylinder, and to connect the fixed cylinder and the tubular member without decentering. In view of this, in the technology disclosed in D1, certain product dimensional precision is required to secure a displacement suppressing effect, and an increase in the number of steps of connecting between the fixed cylinder and the tubular member is unavoidable, which may increase the manufacturing cost.